In conventional optical disc apparatus for personal computers and domestic recorder/player, pickups are liable to be hot because of laser diodes and driving circuits and the like of the laser diodes acting as heat sources. In such a pickup, openings and the like for ventilation are provided in addition to a central opening. The central opening is originally formed in a unit cover disposed on the top of a unit mechanism for storing a pickup, so that disc rotational flows which are air flows induced by disc rotations are guided to the pickup and promote heat dissipation. Examples of this technique are described in patent documents 1 to 3. Optical disc apparatus described in these patent documents include a tray type (patent documents 1 to 3) having a tray wherein a unit mechanism is fixed, protruding to the front of a housing of the apparatus during the mounting/dismounting of a disc, and a top-loading type (patent document 2) of loading and unloading a disc by opening and closing the top cover of the housing of the apparatus. These optical disc apparatus include a unit mechanism which may be exposed outside. In these types, considering a appearance, adherent contaminants, and contact by a user when the unit mechanism is exposed outside, the formation of openings is severely restricted on a part of a unit cover other than the central opening which corresponds to the moving range of the rim of an objective lens for a pickup and a spindle motor for rotating a disc. In the optical disc apparatus of patent document 1, a through hole is provided on a unit cover so as to be placed on a position overlapping the laser driving circuit of a pickup in a plane or placed between a sub guiding shaft and a midpoint between the sub guiding shaft and the objective lens of the pickup, the sub guiding shaft guiding the movement of the pickup. In the optical disc apparatus of patent document 2, a plurality of ventilating holes shaped like a circle, a polygon, a semicircle, a long slit, and so on are provided on a unit cover. In the optical disc apparatus of patent document 3, on a part where the central opening of a unit cover is extended out of a disc mounting area, a tray covering the part has a small thickness at the start in the direction of a disc rotational flow (a large clearance) and has a large thickness on an opening end of the downstream side (no clearances), so that plenty of disc rotational flow is introduced.    [Patent document 1] JP Patent Publication (Kokai) No. 2005-166218    [Patent document 2] JP Patent Publication (Kokai) No. 2005-310192    [Patent document 3] JP Patent Publication (Kokai) No. 2005-322277